Polyurea Grease Research Articles

Enhancement of polyurea grease performance through graphene oxide-functionalized polyurea thickeners: A novel hydrogen-bond network approach

In conventional grease formulations, thickeners and additives are added as distinct components. This study introduces a method that integrates graphene oxide (GO) functionalized polyurea thickeners, creating a unified structure of polyurea and GO. The impact of GO functionalized polyurea on the rheological and lubrication performance of polyurea grease was investigated. Results showed that the polyurea modifies GO by covalent bonds and forms a hydrogen bond network. The GO modified polyurea reduced the yield stress and improved the flowability of the polyurea grease. The GO modified polyurea enhanced the tribological performance of polyurea grease because of the collaboration effect of tribo-chemical film and graphene boundary film. This study emerges as a viable strategy to improve the performance of polyurea grease.

Improving the Oil Separation of Composite Lubricating Polyurea Grease via Regulating the Thickener Network Structure

Improving the Oil Separation of Composite Lubricating Polyurea Grease via Regulating the Thickener Network Structure

Current carrying tribological properties of multi arc ion plated titanium nitride doped silver coating

Sliding electrical contact materials play a crucial role in the transmission and conversion of electrical energy, but due to various factors such as force, electricity, and heat, the interface exhibits complex wear behavior. A single solid or liquid lubrication system can no longer meet the growing performance requirements of current carrying tribology. In this study, a TiN-Ag coating was prepared using multi arc ion plating technology, and a solid–liquid composite lubrication system was formed with ionic liquid and polyurea grease, respectively. Through current carrying friction and wear tests, their tribological properties, electrical contact resistance(ECR) values, and stability were tested, and compared with the results obtained during dry friction. The coating and worn surfaces were analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results indicated that compared with dry friction, TiN-Ag coatings lubricated with ionic liquids and polyurea grease showed higher friction reduction, wear resistance, and conductivity, especially the synergistic effect between ionic liquids and coatings is prominent. The behavior of ionic liquids under voltage was analyzed, and it was found that ionic liquids formed a physical adsorption film composed of a mixture of anions and cations on the worn surface. The ordered layered structure improved the tribological performance of the system.

Effect of ionic liquid modified indium tin oxide as additive on tribological properties of grease

This study investigates the formulation of composite lubricating greases by incorporating SnO2, ITO, and ATO nanoparticles as additives into a polyurea base grease with excellent additive sensitivity, aiming to explore the physicochemical and tribological properties of the composite lubricating greases. Additionally, two categories of three different ionic liquids were selected to modify the nano metal oxides, and the modified powders were characterized to investigate the tribological properties and conductivity of the polyurea grease after incorporating the ionically modified nano metal oxides. The experimental results demonstrate that the nano metal oxides, when used as lubricating grease additives, can form stable boundary lubrication films, exhibiting excellent anti-wear and anti-friction properties. The ionic liquid-modified nano metal oxides exhibit outstanding anti-friction and anti-wear properties, along with increased conductivity. Particularly, the use of lactate-based ionic liquid for modifying nano metal oxides shows superior degradation, anti-friction, anti-wear, and conductivity properties, holding promising prospects for various applications.

Investigating the effects of base oil type on microstructure and tribological properties of polyurea grease

The soaring prices and physiological toxicity of lithium-based grease make polyurea grease a promising alternative due to its balanced cost and performance. Employing preformed thickeners to avoid toxic raw materials has become a preferred method for eco-friendly preparation of polyurea grease. However, the underlying mechanism of base oil modulates the microstructure of polyurea greases prepared with preformed thickeners, subsequently influencing their macroscopic performance remains unclear. Herein, three polyurea greases were synthesized by regulating the base oil types ((poly(α-olefin) oil (PAO40), alkyl naphthalene oil (AN30), and polyether oil (OSP320)) with the same preformed thickener. The real-time polarizing microscope observation of the grease structure evolution process revealed that the preformed thickeners gradually expanded in the base oil and formed a fiber structure. An increased polarity disparity between thickener and base oil leads to a reduced swelling rate and increased fiber length. As a result, compared with high polarity OSP320 and low polarity AN30, non-polar PAO40 induces a more interconnected 3D network composed of long fiber in obtained grease (PG). Low field nuclear magnetic resonance characterization and molecular simulations reveal this network exhibits significant binding ability towards base oil, reducing the movement ability of the base oil, endowing PG with the highest structural strength, achieving effective lubrication and low noise performance. These in-depth understandings will help promote the research and development of polyurea greases.

The effect of thickener structure degradation on tribological properties: Study on the decay mechanism of polyurea grease under mechanical-thermal aging conditions

The aging of lubricants is a primary factor contributing to rolling bearing failures. The rolling stability test simulated the aging behavior of grease under shear and high-temperature circumstances. An investigation was conducted on how mechanical-thermal aging impacts the chemical and physical structures of polyurea grease, as well as how changes in thickener microstructure affect rheological and tribological properties. The results show that under shear and high temperature, structural changes in urea lead to a transformation of the thickener morphologies from the growth of entangled ribbon fiber to a large-diameter rod structure, with a significant decrease in the degree of entanglement. When a certain proportion of fibrous and rod structures coexist, the grease has good oil separation capacity, the structural stabilities of grease become weak, and the deformation resistance decreases. During this phase, the polyurea grease has the best tribological performance.

Tribological Behavior and Mechanism of Surface-Modified Mullite as Polyurea Grease Additive

Abstract The excellent tribological performance of nanoparticles as additives in lubricating greases has attracted widespread attention. In this study, a silane coupling agent (KH550) was used to chemically modify nanoscale mullite (composed of Al2O3 and SiO2), and the modified nano-KH-mullite was dispersed as an additive in polyurea grease at different ratios (0.01, 0.05, 0.07, 0.1, and 0.3 wt%). The friction and wear performance of the compound polyurea greases were evaluated using a four-ball friction tester. Professional instruments will be utilized to analyze the micro-morphology, 3D profile, elemental content, and valence state of the worn surface, aiming to investigate the lubrication and antiwear mechanism of the nano-KH-mullite additive. The results indicate that nano-mullite effectively improves the antiwear and antifriction performance of the polyurea grease. When the additional content is 0.05 wt%, the friction coefficient (COF) and the wear scar diameter (WSD) are reduced by approximately 19.97% and 11.1%, respectively, and the roughness of the worn surface is also reduced. The excellent tribological performance of the composite grease is attributed not only to the good dispersibility of KH-mullite but also to its ability to promote the formation of a composite lubrication film on the friction pair surface. The component KH-Al2O3 in the KH-mullite can fill and repair scratches and grooves on the worn surface, while the other component KH-SiO2 can bear the load and convert the friction mode to rolling friction.

Effects of Erucamide and N-phenyl-α-naphthylamine on the Friction and Torque Behaviors of Grease on Roller Bearings

To evaluate the impact of various proportions of erucamide and N-phenyl-α-naphthylamine on grease’s tribological performance for roller bearings, lithium complex grease (LCG) and polyurea grease (PG) were prepared with erucamide and N-phenyl-α-naphthylamine proportions of (0,0), (0,3), (1,2), (2,1), and (3,0). An investigation was conducted into the microscopic structures of the ten greases and their effects on the friction coefficients and wear scars of GCr15 steel. These findings were validated through bearing friction torque tests. The results indicate that the addition of 2 wt. % erucamide and 1 wt. % N-phenyl-α-naphthylamine to PG/LCG significantly enhances their tribological properties and reduces friction torque, with PG exhibiting superior performance. This enhancement was attributed to the synergistic interaction of erucamide and N-phenyl-α-naphthylamine with the lamellar thickener within PG. Erucamide contributed to friction reduction, while N acted as an antioxidant.

Classification and spectrum optimization method of grease based on infrared spectrum

AbstractThe infrared (IR) absorption spectral data of 63 kinds of lubricating greases containing six different types of thickeners were obtained using the IR spectroscopy. The Kohonen neural network algorithm was used to identify the type of the lubricating grease. The results show that this machine learning method can effectively eliminate the interference fringes in the IR spectrum, and complete the feature selection and dimensionality reduction of the high-dimensional spectral data. The 63 kinds of greases exhibit spatial clustering under certain IR spectrum recognition spectral bands, which are linked to characteristic peaks of lubricating greases and improve the recognition accuracy of these greases. The model achieved recognition accuracy of 100.00%, 96.08%, 94.87%, 100.00%, and 87.50% for polyurea grease, calcium sulfonate composite grease, aluminum (Al)-based grease, bentonite grease, and lithium-based grease, respectively. Based on the different IR absorption spectrum bands produced by each kind of lubricating grease, the three-dimensional spatial distribution map of the lubricating grease drawn also verifies the accuracy of classification while recognizing the accuracy. This paper demonstrates fast recognition speed and high accuracy, proving that the Kohonen neural network algorithm has an efficient recognition ability for identifying the types of the lubricating grease.

Optimization of the Tribological Performance and Service Life of Calcium Sulfonate Complex—Polyurea Grease Based on Unreplicated Saturated Factorial Design

In order to further extend the service life of calcium sulfonate complex–polyurea grease (CSCPG) while ensuring its tribological performance, this article starts with the production of raw materials and the preparation process of the grease and explores the factors that significantly affect the tribological performance and service life of CSCPG based on unreplicated saturated factorial design (USFD). The Kriging prediction model is used along with the optimization objectives of friction coefficient and service life, and nondominated sorting genetic algorithm II (NSGA-II) was used for a multi-objective optimization solution. The tribological and service life tests were conducted before and after optimization. The results show that the viscosity of the base oil and the content of the nano-solid friction reducers have a significant impact on the tribological properties of CSCPG. The content of polyurea thickeners and antioxidants, as well as the thickening reaction temperature, have a significant impact on the service life of CSCPG. When the friction coefficient and service life are optimized as objectives and are compared to the initial group, the friction coefficient of CSCPG could be reduced by 5.3%, and the service life could be extended by 3.8%. The Kriging prediction model based on USFD has high accuracy and can be used to guide the preparation and performance optimization of CSCPG.

On the Optical Assessment of the Structural Degradation of Rheologically Stressed Lubricating Greases

This work explores optical measurements' potential to better understand structural degradation due to the internal friction process of lubricating greases. The samples have been examined as closely as possible to their original state due to the specimen preparation protocol. Eleven model lubricating greases were evaluated for these purposes. Image analysis of transmitted light microscope, SEM and AFM measurements were used to evaluate the grease microstructure under stressed and unperturbed conditions. The results showed that the type of thickener could significantly influence the internal frictional energy due to the structural degradation of the lubricating grease. Thus, the structural skeletons of lithium and calcium greases can dissipate less mechanical energy during a shearing process than polyurea grease or isolated pure biogenic greases.

Tribological Behavior of WS2 Nanoparticles as Additives in Calcium Sulfonate Complex–Polyurea Grease

In order to improve the tribological properties of calcium sulfonate complex–polyurea grease, WS2 nanoparticles were used as additives to prepare WS2 calcium sulfonate complex–polyurea grease. The tribological behavior of WS2 grease on the GCr15 surface was systematically studied. The results indicate that WS2 nanoparticles can significantly improve the extreme pressure performance of calcium sulfonate complex–polyurea grease. When the concentration of WS2 nanoparticles is 2 wt.%, the friction coefficient decreases by 14.94%, and the maximum nonseizure load PB increases by 31.41%. As the temperature increases, the friction coefficient and wear rate of WS2 grease first decrease and then increase. This is mainly attributed to the adsorption and frictional chemical reaction between WS2 nanoparticles and the matrix.

Rheological behaviors and tribological properties of nano-silica grease: A study compared with lithium grease and polyurea grease

Traditional greases gradually cannot meet the performance requirements of high efficiency lubrication, and new nano-thickener greases are expected to be a promising lubricant. This work prepared nano-silica grease (NSG) with a stable structure using nano-silica as the thickener. The physicochemical properties, rheological behaviors and tribological properties of the grease were analyzed, and the results were compared with those of lithium grease (LG) and polyurea grease (PG) commonly used in the market. The results show that NSG has a short chain agglomeration microstructure that can quickly respond to the external environment through structural adjustment. Compared with LG and PG, NSG has the better rheological and tribological properties. These findings will help promote the development and application of new nano-thickener greases.

Facile formulation of graphene oxide modified commercial polyurea grease and its enhanced tribological capability under extremely high contact stress

Grease lubricants have been widely applied to the rubbing components to increase the operation stability and reliability. In this study, graphene oxide modified polyurea grease was prepared by formulating different amounts of exfoliated expandable graphite (EG) into commercial polyurea grease with combined mechanical agitation and grinding processes, tribological characteristics of graphene oxide modified polyurea grease were subsequently evaluated under extremely higher contacting stress. Among all the formulated polyurea grease specimens, polyurea grease with 2.0 wt.% graphene oxide displays better capabilities of minimizing friction and wear. In particular, the wear loss reduces considerably by 80% meanwhile the averaged friction coefficient decreases to 0.10, as referenced with existing polyurea grease. The improved tribological behavior is proposed to be associated with the in‐situ produced graphene oxide solids that enhances extremely lower shearing ability and promotes the fatigue resistance of grease, as well as its desired chemical compatibility with resulting iron sulfide tribofilm. Particularly, graphene oxide works as the dispersed precipitate within the dense iron sulfide/oxide layer induced from ZDDP that covers on the steel substrate.

Effect of Erucamide as Polyurea Grease Additive on Tribological Properties of GCr15 Steel

To investigate the effect of erucamide on the tribological properties of GCr15 steel in this study, polyurea grease is prepared with different concentrations of erucamide as additive. The tribological behavior of erucamide on the surface of GCr15 steel is studied using a reciprocating friction test. The results show that 1.5 wt% erucamide has the best tribological property and friction-induced vibration and noise suppression capability. This is attributed to the formation of a lubricating film on the transition region of the friction surface, which maintains the friction in a relatively stable state, and the maximum thickness of lubricating film is 3.91 μm.

Effect of the grease thickener on tribological properties of Si3N4/GCr15 contact interface and the performance in hybrid ceramic ball bearing

Si3N4 hybrid bearings are considered the most promising motor bearings due to their characteristics of electrical insulation, high speed, low friction coefficient, and wear resistance, which can better meet the requirements of driving motors of electric vehicles. However, the tribological mechanism between the ceramic-grease-steel complex interface is unclear. Three kinds of greases, namely lithium, polyurea, and calcium sulfonate complex grease, were synthesized from poly alpha olefin 40 as base oil. The effects of grease thickener morphology on the tribological properties of Si3N4/GCr15 contact surfaces at different slip speeds were investigated, and the vibration and friction torque performances in 6204 hybrid ceramic balls were evaluated. The results showed that the thickener could form physical deposition film and friction film to protect the worn surface at low speed. The friction and wear conditions were significantly improved at high speed under lithium grease and polyurea grease lubrication, being a mixed lubrication state. In presence of lithium grease, the tribological performance of the Si3N4/GCr15 interface and the vibration performance, impacted condition, starting torque, and friction torque of the hybrid ceramic ball bearings were all the best. Because lithium grease is subjected to continuous shear of the ceramic ball, which releases the base oil stably, and forms a thick oil film with the broken thickener in the center of the raceway, the bearing is in a mild lubrication state. Therefore, for Si3N4 hybrid ceramic ball bearings, lithium grease is a lubricant with good application prospects.

Study on synthesis of biodegradable polyurea grease using modified vegetable oil

Lubricants have been applied in numerous industrial fields, as they help reduce friction and heat generated when operating machines and also protect metallic parts in corrosive environments. In some applications, especially in marine, these greases need to be biodegradable, or they get accumulated and can be harmful to aquatic life. To address this matter, modified vegetable oil was used instead of persistent mineral oil. Also, in submerged conditions, polyurea grease outperforms traditional lithium grease as the latter is more susceptible to water washout. So, in this paper, the polyurea thickener was synthesized in-situ in biodegradable modified vegetable oil by using methylene diphenyl diisocyanate and amines as precursors. The fabricated grease chemical properties were determined by FTIR, and its tribological characteristics were studied by dropping point, penetration, and four-ball test. Results showed that polyurea grease has high operational temperature (dropping point at 278 oC), excellent pumpability (penetration 275 mm-1), and offers great wear resistance (wear load 233 kg).

Modified Ni Nanoparticles as Additives in Various Greases: Assessment of Comparative Performance Potential

China’s rapid industrial development requires more energy consumption based on non-renewable energy resources. The energy consumption caused by unnecessary friction accounts for about 4.5% of the GDP in China. Although grease effectively lubricates machines, lubrication failure may occur under severe conditions. Nanomaterials exhibit intriguing tribological performances and have received much attention regarding lubrication. In this study, oleylamine-modified Ni nanoparticles (OA-Ni) were synthesized and used as lubricant additive in four kinds of commonly used greases: lithium, calcium, composite calcium, and polyurea grease. The OA-Ni were uniformly dispersed in the greases through electromagnetic stirring, ultrasonic vibration, and three-roll grinding. The physicochemical properties and the structure of OA-Ni-doped grease were investigated, while the feasibility of OA-Ni as various grease additives at different contact modes was evaluated by a four-ball friction tester and a UMT-tribolab tester. Tribological tests results revealed that the friction-reducing and anti-wear properties of point-to-point contact were increased by 56.7% and 70.3% in lithium grease, respectively, while those of the point-to-face contact were increased by 59.5% and 68.9% in polyurea grease, respectively. The present work provides not only theoretical guidance of nano nickel modification but also a practical reference for the application of modified nanomaterials to various greases.

Effects of hBN and CaCO3 Nanoparticles on Tribological and Vibration Properties of Polyurea Grease on Rolling Bearing

Effects of hBN and CaCO3 Nanoparticles on Tribological and Vibration Properties of Polyurea Grease on Rolling Bearing

Investigating the rheological and tribological properties of polyurea grease via regulating ureido amount

The ureido amount of polyurea strongly influences the properties of polyurea grease. Here, four polyurea greases (diurea, tetraurea, hexaurea, and octaurea) were synthesized via regulating the proportion and adding order of reactants (diphenylmethane diisocyanate, octadecylamine, and 1,6–ethylenediamine), using polyalphaolefin (PAO 40) as the base stock. The effects of ureido amounts on the physicochemical, rheological and tribological properties were evaluated. More importantly, the correlation of structure and performance characteristics was explored. Results show that the tetraurea with a granular structure presents optimal physicochemical properties and structural strength. The diurea grease with rodlike structure presents the optimal tribological properties due to the synergies of polyurea deposited film and tribolchemical reaction film (ferric oxide and nitrides), as well as oil film.